Derflinger Emiya
by Worldbringer of Joseun
Summary: Illyasviel von Eiznbern had survived the Fifth Grail War and was living peacefully with her brother Shirou until a mysterious object appeared in front of her brother. Curious, Illya examined it only to yanked away in a summoning to a Spring Familiar Summoning Ritual to become the familiar of Louise. Days later, Illya and Lousie make a peculiar discovery in a small shop in Tristin.


Derflinger Emiya

Fate Stay Night & Familiar of Zero Crossover

 _This is a one-shot. Follows the Fate route where Illya lives past the Grail War._

In the capital city of Tristin, lay an average, out of the way sword shop with only an average middle-aged merchant and an average selection.

In most stories, we would focus on the 'average' merchant or perhaps his young shop helper or talentless apprentice who would go on to be very important to the continued survival of the kingdom, the cause of Good, the world, or local damsel in distress or whatever worthy cause is in desperate need of a hero, who is traditionally some poor sucker. But not here.

Here, we do not care about the merchant. We do not care about the shop. We do not care about his family, friends, non-existent apprentice, or shop helper. We do not care about the weapons, weapon selection, weapon suppliers or customers.

Well, the former paragraph was inaccurate. We do care about a certain one-time pair of customers. We do care about a weapon, and no it is not the shiny, jeweled sword made by the best alchemist in the neighboring lands.

Although to say that we care about the weapon is an exaggeration. It isn't the weapon that we are concerned with. We are concerned about what lay within the sword.

The bells on the door chimed as it swung open as two young teenage girls with a warring atmosphere swept into the shop. One of them, a small white-haired albino glared at her slightly taller _(and how that stung!)_ , pink haired companion as the pink-haired girl with a definitely twitching eyebrow continued her argument, "… what I say goes!"

"Why, _of course_ _Master_. If a Servant with superior experience and battle skills were to _disagree_ then I am sure that the Master will be sure to survive the upcoming War by ignoring their Servant," sarcastically drawled the purple and white clad albino. "Far be it from me to actually know how to wield a sword before you waste your family's resources and buy one."

The clashing auras of two angry girls taking the shape of a hulking behemoth of a giant glaring at a strong manticore with outspread wings emerged behind the two girls as the taller of the two squinted and glared at her shorter companion.

The merchant gulped. He had seen similar auras and battlefields between his wife and her enemy at Brimir church whenever he or his fellow merchant across the street failed to steer their respective wife away from each other on worship days. He knew from sad and painful experience that you do not get between the two without wearing armor or preferably something more durable or sacrificial.

But this was his shop and both the pink-haired teenager and the white-haired girl were wearing fine clothes fit for a noblewoman. She was obviously a mage with her insignia declaring her to be a student at the magic academy. Which meant that she knew magic. And she was in his shop. And she was angry enough to potentially light a fireball or magic up a boulder or some other horribly destructive thing and ruin his merchandise!

Bravely, the merchant spoke up in his near tremoring voice, "Welcome to the- "

"You! Get me your best sword!" demanded the pink terror- girl! I mean girl – as she scowled. Yep, the merchant was right, you needed to sacrifice something to get between the two conflicting girls. His bladder control was nearly the sacrifice and only experience with his wife was the difference between nearly and not nearly.

"O-of course! Right away, your ladyship!" the merchant stammered as he ran to his backroom. His best sword was not in there but some of his higher quality weapons would do as sacrifice to her wrath.

His backroom was neat and tidy with the swords hanging neatly on one wall while the axes and polearms hung on the opposite wall. Let it never be said that his wife was not good at cleaning. The merchant paused for a moment to take out his handkerchief and wipe his brow before looking over the collection of swords. His ruby jeweled sword was of poor quality but looked amazing while his gold and silver filigreed sword was at least of decent quality. The sapphire gem short sword-wand was meant to look pretty but be functional for a noblewoman. The second ruby sword with purple amethysts sprinkled alongside the rubies was sub-par in terms of function but the pattern was gorgeous.

The sound of bickering rose from the front room clued in the merchant that whatever he brought out would have to be done quickly. Cursing in his mind, the merchant grabbed the two ruby swords and rushed out to the front. If they started fighting each other, then he could at least loan them the swords and when they broke, insist on payment for breaking his wares.

As he barged through the door, he viewed the unpleasant sight of the two girls glaring at each other from the distance of 10 centimeters away with fingers shaped like claws at their sides, ready to rip each other's throat out. At least it was more civil than the last time he lost sight of his wife on Worship Day.

"Your Ladyship, may I present to you the finest and most valuable swords in my humble establishment," the merchant humbly presented. _And please be rich and do not try to use them on each other until after the purchase!_ "This one is the finest alchemically produced sword from Germania, enchanted to cut through any iron like it were soft butter."

"Yes, thank you. Now which one would you recommend for my familiar- "

"I am NOT your familiar. I am your Servant. And furthermore, I do not need either weapon. It is a waste of my abilities and I cannot use either. These barbarians these days."

"Illyasviel! Just take the sword!"

"Fine, fine," grumbled Illyasviel. "Which sword would you recommend, _Master Louise?_ "

"Hmm," Louise glanced between the ruby sword and the amethyst mixed with ruby weapon. "Take the bigger sword. It will look more impressive."

"I wouldn't take either. Neither one is a genuine sword," a low male voice interjected from nowhere.

The shopkeeper scowled, "Derflinger, I told you not to interact with the customers!"

"Where is that voice coming from?" snapped Louise.

"Over here," came the voice from a … barrel? A barrel which had a sign reading "Discounted weapons".

"Yes, here," one of the swords jingled among them.

"OOOOOH!" exclaimed the short albino as she rushed over to the jingling sword. "Is this a sentient Mystic Code! One capable of talking! But how? Is it projecting into the mind or vibrating at such speeds that it can manipulate the air or is it using the air element to create soundwaves?"

"Uh, miss, that sword can't do any of that. I am _this_ sword," apologetically came the voice from the barrel again as he jingled around.

"I know that!" exclaimed the albino as she flushed and hurriedly jammed the sword in her hands back into the bin before grabbing the real talking sword. "I was just- just, showing off the difference to Master Louise there."

The merchant concealed a smile. His 5-year-old daughter acted like that sometimes. Like when she made a basic mistake of skipping over 7 when counting to ten. However, that annoying sword was less cute.

"Derflinger, keep quiet and don't ruin this deal!" yelled the merchant. Then he turned to his more sensible customer who was oohing over Derflinger "Now as I was saying, this other sword is one of the finest blessed swords straight from Romalia. No undead will be able to stay in the presence of this fine sword and it will provide warning against any undead nearby." ' _If only because the sword pushes away from any form of necromancy.'_

"Get away from that sword Illyasviel. I will _not_ have my familiar walk around with a poor discount blade when there are better swords here," Louise snapped.

"But it is a talking sword! A sentient Mystic Code! Do you even know how rare those are! Why with this, big brother would…" she cut off, her bright expression darkening into sorrow.

"Is your brother some kind of sword collector? Because I don't like sitting in a case for decades. Deadly dull, no way I would go through it again," commented Derflinger.

"No, no," Illyasviel said, forcing a smile which didn't quite reach beyond her lips. "He was a good, kind boy. Naïve and foolish but very, very kind."

"Until someone ripped me from my brother!" Illyasviel glared at Louise who glared right back.

"As I told you before, I didn't choose _you_ as my familiar. It was the ritual and even if I could choose, I wouldn't ever pick you!" Louise shouted back.

"And I didn't know that your Formal craft sets up a trap that would suck me in while investigating it! What kind of ritual just uses falling for a trap as its qualification for a summoning! You only get stupid idiots that way! And you should always set up a target and a method and understand what you do and a reason to follow your orders, otherwise you run the risk of not only killing yourself by summoning something so much stronger than yourself but bringing down a Sealing Designation on your head!" Illyasviel retorted.

If this had been intended to calm down or even quiet the other girl, then it couldn't have been a bigger failure. "Shut up! Don't you dare speak of the Founder's Springtime Summoning Ritual in that manner!" Louise straightened her back up to get even taller, well at least as tall as she could, took out her wand and pointed it at the younger girl. "Familiar! If you will not cease such blasphemous talk, then I will-!"

When the wand had come out, the merchant had had enough, "Noble Ladies, please I implore of you, do not argue in my store and out in public! Think of what your dearly beloved mothers" Illyasviel tensed up and her eyes flashed at that but the merchant was on a roll "and family would say, of how they would react to the shame of such a public squabble! Let us instead have peace and buy the sword on the way out."

Now this would have been an impressive sight if anyone came into the store at this moment. A brave merchant, both in-between and taller than the two young ladies who were obviously of nobility, holding forth his hands in a gesture of imploration towards them both while one clutched a big black sword looking like she would like nothing better than to use it as a club on the other girl who wore the flaring cloak of a mage, who in return held her at wand point as if she was about to release some great fireball.

It was fit for a picture. And the name of the picture would be "Why France was the First Place to Kill off all their Nobility" when you considered that the backdrop was dozens of different weapons all owned by the one merchant.

Internally, and without any sign that potential revolutions could be next in the historical time axis, the merchant was a different story. ' _Please, oh please, oh please Brimir make it so that they don't set me and my shop on fire! I haven't been able to pay my fire insurance yet and it doesn't cover acts of nobility spurred on by insane talking swords! I have heard that being burned to death is a most painful death! I pay my tithes and I don't want to die at the hands of your teenaged nobility! '_

You see, while the two noble girls had been escalating their fighting up to near violent levels, the sword had begun laughing hysterically. Now that the words of the arms dealer had bought a few seconds of peace, it interjected, "Ha Ha Ha! Now you two get along as funnily as some of my previous masters! Ha ha ha! You two will just be a barrel of laughs! He he he! Hey shop owner, sell me to these two! It'll be much than sticking around in this boring shop all day."

The merchant's hopes rose. Neither lady had yet to destroy his shop, create a mess, or kill each other and it looked like he might finally be able to get rid of Derflinger! "Oh yes, this sword is a real bargain! Only 100 Écu and as you can see it is in good condition despite years of service on battlefields, meaning that you won't need to worry about it breaking," The merchant said scurrying around to the back of the counter, dropping the two swords on the counter, ignoring the mutter of something like "Structural Analysis" in Albonian coming from the red-eyed albino. _'what a strange phrase. Never mind, just get them out of my shop!'_ "Let me just ring you up and you lovely young ladies can be on your way."

Louise sniffed, "No thank you, we would prefer a weapon of better quality and actual– "

"Louise."

Louise glanced over towards Illyasviel whose white skin seemed to have gotten a shade whiter and was now clutching Derflinger to her chest almost as if she were trying to hug it. Fortunately, the blade was still sheathed.

"Louise, if you will buy this sword then I will consent to being your Servant for the rest of my life."

Louise paused. Illyasviel's offer was entirely unexpected. Since her summoning a week ago, Illyasviel had demanded, insisted, and even fought to go and get back to her home. Now she was giving all that up for a plain, simple talking sword? What could be so valuable about that sword? But to keep her familiar…

"Will you actually do that? Will you serve me as my familiar without complaint for the rest of your life?"

Illyasviel looked up, her eyes full of resolve, as she swore "I swear by my magic circuits and as the 6th head of the Emiya family that I will serve Louise as her familiar for the rest of this life if she will give this sword to me."

Louise felt her gaze hold on Illyasviel's steely, determined red eyes. She doubted it. She wanted to doubt it. But there was something in Illyasviel's eyes, not a pleading look but instead a pleading, yet demanding, look that said come Brimir or elves, Illyasviel will not be denied and that she was just as sincere in this one thing than even when she stated that she would go back to her brother.

Louise slowly nodded, her heart beating in sympathy, and turned back to our anxious merchant and said "We'll buy that sword. 100 Écus, wasn't it?"

[page break]

The merchant sighed, wiped his brow, and slouched against the doorframe. That had been one harrowing experience. Usually when nobility enters his shop, they don't come in with the intention to use his swords right away. And these two were but a short step from starting a full-blown feud inside his store!

Shaking off his sweat and trying to calm his racing heart, he returned to his seat behind his counter only to see two jeweled swords in the open space on his counter.

He howled. _NO! I forgot to sell the masterpieces!_

As the merchant lamented the loss of his potential fortune, Louise and Illyasviel walked down the street, Louise eyed the battered sword like it was repulsive and asked "Why do you want _that_ sword of all things?"

Derflinger cackled, "Why it is because I am the best sword! You won't find a smarter or sharper sword than me anywhere!"

Illyasviel, who still clutched the sword as if it were the most precious thing in existence to her, said nothing but a small tear escaped her eye. She jerked her head to the side to hide from her new master who was once again examining her new familiar but said nothing more.

[page break]

As night fell, Illyasviel clad in a nightgown, sat head turned down upon her small bed in the corner, still holding and stroking Derflinger who was mercifully quiet since Louise in her 4-corner bed was fast asleep. Of course, Derflinger could just have realized that Illyasviel was troubled and needed something calming to do. Who knows? He wasn't telling. Typical big brother.

Illyasviel raised her eyes to the window, a fierce and angry light shining in her eyes. She latched onto a star and whispered, "Whoever did this to my brother, I will rip your spirit from your body, stick it inside a doll, force you to watch as I rip your entrails out, stuff them down your throat. Then I will destroy everything you hold dear and whatever thing you wanted to learn by doing this to my brother and only after that will I slowly set your doll on fire one thread by one thread so that your agony will last a very, very long time."

Derflinger whistled softly, "Don't know what made you this angry but that is definitely one of the scariest threats that I have ever heard."

Illyasviel set her sword down next to her pillow before lying down beneath her covers and pulled her new sword snuggly against her before whispering, "Don't worry about it big brother, I will never hurt you. Even if you forgot who you were and that you are my big brother." Her eyes drifted shut. "But tomorrow, I will … start … looking… for them… to get … my vengeance…"

[page break]

 **Now I know some of you are going** _ **"This isn't how Illyasviel/Louise acts!"**_ **but I have a reason for it. Illyasviel was ripped from her brother one or two months after the 5** **th** **Grail War, when she has less than a year to live. She is** _ **very**_ **upset about that. Also, she and Louise have trouble getting along and this is a week or so after they first meet, frustrations have been building up for both of them. It doesn't help that they come from different magic systems and cultures and that Illya is taking some of her frustrations out on Louise.**

 **And then Illya meets Derflinger. Derflinger which is a spirit of a sword. Derflinger which was forged from the spirit of a summoned Shirou about 6000 years ago. Illya's Shirou responded to the summoning since he figured it would increase his chance to find either Illya, who was summoned a few weeks before or Saber who he is in love with, but he ended up in the long-distant past of Familiar of Zero while Illya ends up in Saito's place. To Illya, this is unforgivable and she will adopt this as her new purpose just like how she used Kiritsugu abandoning her as her purpose for the Fifth Grail War.**

 **This is a one-shot. If anyone wants to take this up and run with it, feel free. Just let me know so I can point others to it.**


End file.
